Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating. The table gives the bond energies. | bond | bond energy/kJ mol⁻¹ | |------------------|----------------------| | P–Cl (in both chlorides) | 330 | | Cl–Cl | 242 | What is the enthalpy change for the decomposition of PCl₅ to PCl₃ and Cl₂?

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Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating - CIE - A-Level Chemistry - Question 8 - 2016 - Paper 1

Question 8

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Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating. The table gives the bond energies. | bond ... show full transcript

Worked Solution & Example Answer:Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating - CIE - A-Level Chemistry - Question 8 - 2016 - Paper 1

Step 1

Calculate the energy required to break bonds in PCl₅

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Answer

For the decomposition reaction of PCl₅ into PCl₃ and Cl₂, we need to break the P–Cl bonds. In PCl₅, there are five P–Cl bonds. Thus, the total energy required to break these bonds is:

$5 imes 330 ext{ kJ mol}^{-1} = 1650 ext{ kJ mol}^{-1}$

Step 2

Calculate the energy released from forming bonds in PCl₃ and Cl₂

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Answer

In the products, PCl₃ has three P–Cl bonds, and Cl₂ has one Cl–Cl bond. The energy released from these bonds is:

$3 imes 330 ext{ kJ mol}^{-1} + 242 ext{ kJ mol}^{-1} = 990 ext{ kJ mol}^{-1} + 242 ext{ kJ mol}^{-1} = 1232 ext{ kJ mol}^{-1}$

Step 3

Calculate the overall enthalpy change

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Answer

The overall enthalpy change (ΔH) for the reaction can be calculated by subtracting the energy released from the energy required:

$ΔH = ext{Energy required} - ext{Energy released} = 1650 ext{ kJ mol}^{-1} - 1232 ext{ kJ mol}^{-1} = 418 ext{ kJ mol}^{-1}$

Thus, the enthalpy change for the decomposition of PCl₅ to PCl₃ and Cl₂ is +418 kJ mol⁻¹.

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Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating - CIE - A-Level Chemistry - Question 8 - 2016 - Paper 1

Worked Solution & Example Answer:Gaseous phosphorus pentachloride can be decomposed into gaseous phosphorus trichloride and chlorine by heating - CIE - A-Level Chemistry - Question 8 - 2016 - Paper 1

Calculate the energy required to break bonds in PCl₅

Calculate the energy released from forming bonds in PCl₃ and Cl₂

Calculate the overall enthalpy change

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